Highly Active Fe Sites in Ultrathin Pyrrhotite Fe<sub>7</sub>S<sub>8</sub> Nanosheets Realizing Efficient Electrocatalytic
Oxygen Evolution
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Abstract
Identification of
active sites in an electrocatalyst is essential
for understanding of the mechanism of electrocatalytic water splitting.
To be one of the most active oxygen evolution reaction catalysts in
alkaline media, Ni–Fe based compounds have attracted tremendous
attention, while the role of Ni and Fe sites played has still come
under debate. Herein, by taking the pyrrhotite Fe<sub>7</sub>S<sub>8</sub> nanosheets with mixed-valence states and metallic conductivity
for examples, we illustrate that Fe could be a highly active site
for electrocatalytic oxygen evolution. It is shown that the delocalized
electrons in the ultrathin Fe<sub>7</sub>S<sub>8</sub> nanosheets
could facilitate electron transfer processes of the system, where
d orbitals of Fe<sup>II</sup> and Fe<sup>III</sup> would be overlapped
with each other during the catalytic reactions, rendering the ultrathin
Fe<sub>7</sub>S<sub>8</sub> nanosheets to be the most efficient Fe-based
electrocatalyst for water oxidation. As expected, the ultrathin Fe<sub>7</sub>S<sub>8</sub> nanosheets exhibit promising electrocatalytic
oxygen evolution activities, with a low overpotential of 0.27 V and
a large current density of 300 mA cm<sup>–2</sup> at 0.5 V.
This work provides solid evidence that Fe could be an efficient active
site for electrocatalytic water splitting